Jury selection began Tuesday in a defamation trial against billionaire Elon Musk.
The suit is brought by a British cave explorer over a Tweet by the Tesla CEO calling the Brit a pedophile.
Vernon Unsworth was part of a team hailed as heroes for rescuing 12 boys trapped in a flooded cave in Thailand last year.
At the time, Musk offered the use of a mini submarine.
Unsworth later told CNN that offer was a PR stunt.
Musk lashed out at Unsworth on Twitter, calling him "pedo guy." He later apologized.
But Unsworth says the insult harmed his reputation, and wants a court to force Musk to pay punitive damages.
Lawyers for Musk say the tweets were just his opinion, and that Unsworth can't show harm.
It's not the first time Musk's Twitter use has landed the entrepreneur in trouble.
He reached a settlement with the Securities and Exchange Commission last spring after Musk stunned Tesla investors with a tweet that he was considering taking the company private.
With nearly three million followers, Musk's Twitter account is a major source of publicity for his Palo Alto, California-based electric car company, which does not advertise.
The defamation trial in Los Angeles is scheduled to last about five days.
Musk is expected to take the stand in his own defense.